Flood warning

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Under flood warning or flood warning means the warning before an expected flood - in coastal areas such as inland waters - and its effect by sprawl and flooding . They belong to one of the areas of responsibility in flood management as a sub-area in disaster control . Flood warnings are of great public interest and important in the risk management of natural hazards . From high-level alarm One speaks specifically in taking protective and defensive measures.

Flood warning services

Under flood warning service (flood warning service, Flood Information Service) refers to specific officially-official or private service providers that issue flood warnings for a certain range.

The warning services operate or use a gauge network and determine the risk of flooding on the basis of weather forecasts , the flood warnings in the catchment area and knowledge of the water system, and write the necessary warning messages.

The flood warning service is usually an activity of the hydrographic services , in some places there are special flood warning services (as in the German states or in France ), elsewhere all environmental warnings are centralized (authority for disaster management , as in the Austrian federal and state warning centers, otherwise at a general one Environmental authority ). The flood warnings are also issued consistently via weather services (these are often linked as a hydrometeorological service ), and increasingly also internationally networked ( e.g. with the European network meteoalarm or level alarm ): On coasts of the sea, a connection with storm warnings is necessary due to the storm surge problem , inland there is one Flood warning depends on precipitation forecasts, in high mountains also on temperature rises and snowmelt . Flood warning services are often in connection with a shipping authority (such as the federal level in Germany or on the Danube in Austria) . The flood warnings are also distributed via shipping information systems , which are also increasingly networked internationally ( e.g. KHR-GIS on the Rhine). The tsunami warning systems are a special case ; in addition to the hydrographic problem, they establish a connection with geophysical services and their earthquake warnings or warnings in the event of volcanic eruptions .

Flood warning levels

General warning levels

Verbal descriptions such as “small flood”, “medium flood”, “large flood” have grown historically. These are geared towards phenomenological effects, such as overflow, flooding of barrages or the extent of the flooding.

Today, the warning levels are consistently linked to the annuality of a flood event, for example a (calculated) flood of the century , as a discharge amount (HQ100 for short) or water level . The assessment basis is usually a historical reference value, which does not exclude the accumulation of events classified as centenary. That is why the mean flood  (MHQ) is not used for warning levels, it is averaged over a certain series of data that is usually too short to have recorded rare extreme events.

In terms of the language used for Central Europe, one can say that a "small" flood every 2 to 5 years, a "medium" flood every 10 years, a "large" flood every 30 years and a "very large" flood every 100 years occurs.

Overview of the warning levels in German-speaking countries
Germany (DE) Austria (AT)
Warning levels (AT)
Switzerland (CH)
> MQ Elevated mean water (increased water flow)
very common
1: No or little risk
> HQ1   1 Small floods
> HQ2 Small flood
warning level 1 (start of reporting)
2: Moderate risk
> HQ5 Medium flood
> HQ10 Medium flood
warning level 2 (control service)
2 Large floods are
3: Considerable danger
> HQ20 Large flood
warning level 3 (security service)
> HQ30 3 Very
seldom very large floods
4: Great danger
> HQ50 Very large flood
warning level 4 (flood defense)
> HQ100 Extreme floods
extremely rare
5: Very great danger
Classification of runoff during floods in June 2009 (Austrian system, here in different colors than the table above: red> HQ100 )
  • (DE)Four-level system of the German transnational portal hochwasserzentralen.de ; corresponds to the (flood or storm surge) reporting levels or alarm levels of the federal states (Hamburg: only 2 levels; Hesse, Lower Saxony, North Rhine-Westphalia: only 3 levels); see flood warning levels in Germany
  • (AT)In Austria 3-part scale flood warning levels (discharge categories ) of the hydrographic service of the federal eHYD : the 6-level system, which is important for small and mountain streams, is particularly common in Burgenland, in Carinthia, Tyrol and Vorarlberg.
    The system continues to bottom:
    <MQ:  low - to middle water / very often , <MJNQ ( mean annual low flow ): Extreme low water / rare ; Burgenland uses warning mark 2 on the mean of MQ and HQ1, especially for Lake Neusiedl, warning mark 1 at Q95% ( <Q95% ) because of the transnational work of the Austro-Hungarian Waters Commission . Data are currently generally related to the period 1981–2010 hydrographic year (30-year mean). 
  • (CH)Swiss hazard level system of the Federal Office for the Environment (FOEN); the threshold values ​​are selectively adjusted in consultation between the federal government and the cantons.

Local warning levels

Hamburg-St.Pauli gauge: top right, the local storm surge levels in relation to the level value

Warning levels at a certain point are mostly based on many years of experience and are typically measured at a level . Here you know which water level has which damage potential. Without precise knowledge of the level itself, i.e. level zero, normal water level and the course of the rise (hydrograph) and the discharge regime on site, pure water level information such as "6.32 m level XXX" are worthless. For local disaster control, the water level and its rise (mostly in cm / h ) are the central alarm signals.

Special warning levels are, for example:

  • In Switzerland, the FOEN uses a hazard level system for the lakes in the form:
    Summer level (SK, maximum annual mean) to high water limit (HWG, a local empirical value) within the limits SK + 13 ( hazard threshold 1 ), SK + 23 ( hazard threshold 2 ), HWG ( hazard threshold 3 ) and HWG + 25 cm ( hazard threshold 4 )

See also: Meteoalarm , European warning association of national and regional warning levels

Individual evidence

  1. Warning in the event of a disaster: Flood warning , help.gv.at
  2. a b "H" in this hydrographic notation stands for "hoch, high", "Q" generally for the discharge ("quantity"), the number denotes the annuality; also written as HQ 100 ; corresponding to about "M" for 'middle, mean'.
  3. Notes on the Internet offer, cross-border flood portal hochwasserzentralen.de , accessed on August 3, 2014.
  4. Current level data of Austrian waters , information sheet on the eHYD service: Current Level , Ministry of Life, Section The discharge categories : Flood , p. 2 f (pdf, ehyd.gv.at, accessed on Aug. 3, 2014)
  5. a b The water level stations on the rivers , Burgenland water portal, accessed 3 Aug 2014;
    Q95% describes the low water value that is reached or exceeded 95% of the time, i.e. below it on about 18 days (which corresponds to the meteoalarm scale).
  6. a b Current runoff situation on Carinthia's rivers : legend , Hydrographic Service - Carinthia;
  7. ^ Hydro online: Wasserstand '→ Explanations: Information on the water level marks in the classification and the hydrographic map , Hydrographischer Dienst Tirol, tirol.gv.at
  8. ^ Discharge measuring stations in Vorarlberg : Legende , Land Vorarlberg; each accessed on Aug. 3, 2014.
  9. a b The 5 danger levels for floods , Federal Office for the Environment, accessed 3 Aug. 2014.